Solvent refining of naphthas



Sep@ 23, i954 H. sHALn' ET AL SOLVENT REFINING OF NAPTHAS Filed Dec. 19. 1949 w e., R. N mhmm E 0 ei r N 6 .A www m Y HJAB Patented Sept. 28, 1954 STATES PATENT OFFICE SOLVENT REFINING OF NAPHTHAS Application December 19, 1949, Serial No. 133,753

9 Claims.

This invention relates to a process for refining naphthas containing olens, saturates, aromatics and sulfur compounds. More lparticularly it relates to a combination process for rening high sulfur cracked naphthas, for example catalytically cracked naphtha or thermally cracked naphtha, including coke still naphtha.

It is known that cracked naphthas have a high proportion of olenic and aromatic compounds. A high concentration of sulfur in these naphthas, i. e. above 0.15% S, is deleterious to their use as high octane gasolines, because of the poor lead response of sulfur containing stocks, and because of the corrosion, excessive engine Wear and other deleterious effects clue to the acid gases produced in the combustion of sulfur compounds. It is, therefore, desirable to remove the sulfur compounds from high sulfur cracked naphthas While retaining as much as possible of the high octane olefinic and aromatic hydrocarbons.

Solvent extraction with various conventional solvents, e. g. furfural, nitromethane, has been proposed as a method for desulfurization of cracked naphthas. These solvents extract aromatics proportional to the amount of sulfur extracted, so that production of low sulfur naphthas is attended by high aromatic loss, resulting in low raflinate yields of relatively low octane value.

Another method of cracked naphtha desulfurization is extraction with substantially anhydrous hydrogen fluoride. This method provides excellent desulfurization, as Well as a good separation between aromatics and sulfur compounds. However, the process is attended by high extract losses due to the conversion of olens by such processes as polymerization, alkylation, hydroiiuorination, hydrogen disproportionation, etc. Another disadvantage of the HF' extraction process is the alkylation of the aromatics by the olens present in the naphtha, resulting in the production of materials boiling above the boiling range of gasoline.

Still another proposal for the desulfurization of cracked naphthas has been the hydrogenolysis of the sulfur compounds, the so-called hydrofining process. If this process is applied to cracked naphthas containing large amounts of olefinic materials, hydrogenation of the olens occurs along with the hydrogenolysis of the sulfur compounds. The direct application of the hydrofining process to cracked naphthas entails a high and uneconomical consumption of hydrogen and results in an excessive decrease in octane ISG-14.15)

2 number due to the hydrogenation of oleflns to form parains. A related process, the autoning process, which employs in situ dehydrogenation of naphthenes as the principal source of hydrogen, retains the disadvantages of the hydroning process with the added disadvantage that naphthenes are usually present in low` concentrations in cracked naphthas.

One object of our invention is to provide a process for refining high sulfur cracked naphthas. Another object of our invention is to provide a combination process for rening naphthas containing olefins, saturates, aromatics and sulfur compounds, which process will result in the substantial elimination of sulfur compounds with minimized loss and conversion of the other components of the naphtha feed stocks. An additional object of our invention is to provide a process for the selective desulfurization of high sulfur olenic-aromatic naphthas. These and other objects of our invention will become apparent from the ensuing description thereof.

Briefly, the process of this invention involves treating a 4-component naphtha., as above described, to produce a fraction comprising predominantly olens and saturates and a second fraction comprising predominantly aromatics, sulfur compounds and a minor proportion of olefins, based upon the amount of oleflns present in the naphtha charging stock; treating the second fraction With liquid hydrogen fluoride under conditions adapted to eifect substantial desulfurization of said second fraction to produce a low-sulfur highly aromatic rainate; blending the lowsulfur aromatic rainate derived from HF treatment with the olens-saturates (first) fraction derived from the initial treatment of the 4-component naphtha to produce a low sulfur high octane number naphtha. The above-described process can be greatly enhanced in practical value by subjecting the HF rafiinate to fractional distillation to produce an extremely low sulfur naphtha distillate and a relatively high sulfur gas oil fraction and by blending only the naphtha distillate fraction With the olens-saturates fraction produced upon initial treatment of the Ll-component naphtha charging stock.

The invention is applicable to high sulfur olenic-aromatic naphthas generally, i. e. to naphthas in which the olelin to paran ratio is in the range of about 3:1 to 1:3 and is particularly advantageous for charging stocks in which the olefinic content exceeds the parafnic content. By high sulfur, We mean a sulfur content which is at least about 0.15 per cent and which is usually in the range of about 0.25 to '1 percent, by weight, or even more. By naphtha, we mean a normally liquid hydrocarbon fraction boiling below 450 F. and usually boiling almost entirely within the range of 106 to 400 F. An outstanding example of a high sulfur olenic naphtha is the naphtha produced by the coking of high sulfur reduced crude in any known manner such, for example, as by continuously introducing heated charging stock into a coke drum at about atmospheric pressure to 50 pounds per square inch at a temperature in the range of about 850 to 950 F., and continuing the operation until coke solidifies in the drum, the vaporous products from the drum being fractionated into a coke still naphtha fraction and one or more heavier fractions. The invention is also applicable to the refining of high sulfur olenic naphthas produced by thermal cracking or by catalytic cracking.

Coke still naphtha has an olen to paraflin ratio of approximately 2:1, and contains from about 0.25 to 4 per cent of sulfur by weight, a representative stream containing, for example, about 1 weight percent of sulfur. The bromine number of the olefmic components of a representative coke still naphtha may be about 70 to 85 but there is a bromide absorption due to sulfur corresponding to about 5 bromine num-bers perweight percent sulfur.

The separation of the Ll-component naphthas of the kind here under consideration in order to produce an olens-saturates fraction and a fraction comprising predominantly aromatics and sulfur compounds together with a relatively minor proportion of oleflns, respectively, can be effected by certain selective solvent extraction processes or adsorption proceses. Suitable selective solvents comprise N,N-dialkyl-formamides boiling below about 250 C., particularly dimethylformamide and diethylformamide; alkylsulfolanes, furfural, phenol, liquid SO2, nitromethane and other known selective solvents.

Dimethylformamide is one of our preferred solvents, and although it boils at 153 C., which is within the boiling range of the naphtha feed stocks, it can be readily separated from raffinate and extract by simple water washing and then separated from water by simple distillation since it does not form azeotropes or constant boiling mixtures with water. Such a solvent is heat stable, will not polymerize or form tars when heated, is non-corrosive and is completely miscible with water. In addition, its density of 0.945 (D254) permits ready gravity separation from petroleum stocks. For optimum results, the dimethylformamide should contain a small amount of water which should be less than 25 percent and is usually in the range of about 1 to 10 percent, or approximately 2 percent by volume when the ratio of solvent to oil is of the order of 1, larger water contents being permissible with higher ratios of solvent to oil. r.he water is very effectively utilized when introduced into the extract portion of a countercurrent extraction system. Thus, when a countercurrent tower extractor is employed, a small amount of the water is most effectively utilized when introduced into the extract phase near the point of charging stock inlet or between this point and the bottom of the tower. The invention is not limited to tower type extraction, however, and the extraction may be effected batchwise, in a multiple batch system, in a countercurrent batch system, or by any other extraction method knownto those skilled in the art.

The extraction can best be carried out with a volume ratio of dialkylformamide, e. g. dimethylformamide, to charging stock in the range of 0.2 to 3, the preferred range being about 0.5 to 2. The extraction may be effected at ordinary room temperature or within the range of about -10 to 100 C., preferably about 10 to about 50 C. The pressure should be sufficiently high to keep all material in liquid phase.

Another preferred selective solvent for use in the first stage of our process is 2,4-dimethylsulfolane, which boils at about 281 C. and which thus can be readily separated from naphtha raffinates and extracts by simple distillation. For optimum results, the dimethylsulfolane should contain a small amount of water which should be less than 10 percent and usually in the range of about 1 tc 5 percent or approximately 2 percent, by volume, when the ratio of solvent to oil is of the order of 1. With higher ratios of solvent to oil, the water content may be as high as 15 percent, by volume. The water is most eectively utilized when introduced into the extract portion of a countercurrent extraction system. |The extraction with alkylsulfolanes, such as 2,4-dimethylsulfolane, can best be carried out with a volurne ratio of solvent to charging stock in the range of 0.3 to 3, the preferred range being about 0.5 to 1. The extraction may be effected at ordinary room temperature or within the range of about 10 to 100 C., preferably about 10 to about 50 C., and the pressure should be suiicient at least to maintain the liquid phase.

The following data were obtained when a coke still naphtha of about bromine number containing 0.9 weight per cent sulfur was extracted at room temperature at a 1:1 solvent (volume) ratio with ZA-dimethylsulfolane having the indicated water content. The following results were obtained in the single batch extraction.

xivgteerrciet V. Percent Wt. Percent Wt. Percent Desulfuriza- Dimemyr .Rafmte ,Sulfur m Desuifulitien 1 Sulfolane Recovered ltoihnate zation Selectivity 0 70 0. 46 49 1i 5 l 2 76 0. 47 48 2,0 5 s2 o. 5o 45 2. 5 I 1 i Percent desulfln'ization divided by treating loss.

Portions of the same charging stock were countercurrently extracted in a column at room temperature at a 1:1 volume ratio of 2,4-dimethylsulfolane to naphtha (the water being introduced at the top of the column when water was used) and the following data were obtained:

Percent Percent Percent Percent Desulurizs.- Water 1n Ramnatc Sulfur in Dcsulfurition Solvent Recovered Ralhnate zation selectivity a bromine number of about 75, and the extract a bromine number of about 91. Since one weight percent sulfur in organic sulfur products is equivalent to about 5 bromine numbers, the bromine number of the feed may be broken down to a bromine absorption by olens corresponding to about '75 and a bromine absorption due to sulfur corresponding to about 5. Since the ranate contained 0.25 weight per cent sulfur, a similar analysis indicates a 74 bromine number for the olefin content thereof. The extract, on the other hand, contained about 2.5 weight per cent sulfur so that the olen content thereof apparently had a bromine number of about 78. These data show that there is no appreciable separation of oleiins from paraiins, i. e. no appreciable selectivity of ZA-dimethylsulfolane for oleiins when the solvent is employed for extracting a high sulfur olenic naphtha.

It should be pointed out that since the oleiinic naphtha, rafiinate and extract are lower boiling than the 2,!i-dimethylsulfolane solvent, separation of this solvent may be effected by simple distillation, although any final traces of solvent may be removed by water scrubbing if desired. An important feature of dimethylsulfolane in extracting high sulfur oleiinic naphtha is the fact that the solvent does not cause any condensation, polymerization or alkylation and does not combine with the olefins (as is the case, for example, with hydrogen fluoride and certain other solvents).

An important feature of our invention is the remarkable effectiveness of 2,4-dimethylsulfolane for removing from a high sulfur oleiinic naphtha an extract which contains such a relatively large proportion of the original sulfur, but only a relatively small proportion of the original olefins. Thus, in the above countercurrent extraction example, if the per cent sulfur divided by the corrected bromine number of the high sulfur oleiinic naphtha, raffinate and extract, respectively, are compared, it will be found that this measure of sulfur to olefin ratio is 0.012 with the original high sulfur olenic naphtha, 0.003 in the case of the raiiinate and 0.03 in the case of the extract, the ratio in the case of the extract being ten times that in the case of the raiiinate and about three times that in the case of original charge.

The employment of silica gel to effect separation of li-component naphthas to produce an olens-saturates fraction and a second fraction comprising aromatic sulfur compounds and a minor proportion of olefns has been described (S. Eagle and C. E. Rudy, Jr., paper presented before a joint symposium on Adsorption and the Division of Petroleum Chemistry, American Chemical Society, Atlantic City meeting, September 18-23, 1949).

Following the treatment of the 4-component naphtha to produce a fraction comprising predominantly aromatic and sulfur compounds containing a minor proportion of olens, based on the olens charged with the naphtha feed stock, the fraction thus obtained is subjected to treatment with liquid substantially anhydrous hydrogen fluoride to produce a low sulfur high-aromatic raffinate and a high sulfur extract. In a preferred form of our invention only the naphtha fraction of the railinate derived from HF treatment is blended with the olefin-saturates fraction produced in the rst-stage treatment of the 4- compcnent naphtha. The hydrogen fluoride treatment can be effected at temperature between '-10 and1001C., preferably about 10 to about 50 C., employing HF in an amount sufficient at least to produce a distinct acid phase, e. g., between about 5 and about 200 volume per cent of HF, preferably about 10 to about 50 volurne per cent of HF, based on the hydrocarbon fraction being treated, under a pressure sufficient to maintain the liquid phase. The hydrogen fluoride treatment can be effected in conventional equipment, for example in concurrent or countercurrent extraction column or agitator-settler equipment combinations such as have heretofore been employed in HF extraction and alkylation processes. However, countercurrent column treatment is preferred.

The following example will illustrate one embodiment of our invention in which N,Ndimethylformamide was employed as the solvent in the first stage and HF in the second stage. A sample of fluid catalytically cracked stabilized heavy naphtha (wt. per cent S=0.275; octane number, CFRR-l-l cc. of lead tetraethyl=92.9; bromine number :45.5, nD2=1-4487 was extracted at 25 C. in a countercurrent column, containing a contacting section packed with glass beads. The solvent used was N,Ndimethylform amide containing 5 volume percent of water at a solventzoil ratio of 1 and throughout of 15.8 volumes of oil per hour per volume of packed contacting space. The properties of the fractions obtained in this extraction are listed below.

Yield W12.

Vol. y 711,20 Percent Bre No. (29mm No Percent S (UFR R+ l) Ralllat n 58 1. 4295 0. 075 45. 8 80. 2 EXI'lC 42 1. 4708 0. 410 36. 9

Yield, Vol. Percent fo 0 Pwt' in N o rign 2 ercen 1'2 o. gg @IHF mal D s ate Charge Naphtha Charge Gasoline 72. 2 65. 7 27. 6 l. 4729 0. 034 l. 9 Gas Oil 27. E 25. 3 l0. l. 5089 0. 25 4. 7

Entirely unexpected and particularly noteworthy is the fact that the sulfur compounds in the dimethylformamide extract which escaped extraction by HF were concentrated in the gas oil boiling range rather than in the gasoline boiling range. Thus, as the above data show, the concentration of sulfur in the gas oil was almost eight times as high as in the gasoline.

The gasoline fraction derived from the HF raiiinate was ,blended with the dimethylformamide ranate to give a total yield of of gasoline, based on the original naphthaY charged '7 -to the process. vThe properties .-.of the :blended .gasoline product are listed below:

Wt. percent S 0.067 Octane Anumber (CFRR-l-l) 86.6 Bromine number 33.8 1LD20 1.4428 11254 0.777

It will be apparent that the process Iof .our invention in the foregoing .specific instance vresulted in '76% desulfurization of the naphtha charging stock while 77% of the olefins therein were retained in the blended gasoline product.

The same stabilized heavy naphtha, derived vfrom fluid catalytic cracking, as used in the above sequence of steps was .extracted directly with substantially anhydrous hydrogen fluoride and the resultant raiiinate was fractionally distilled to produce -a 400 F. end point gasoline and a gas oil fraction. The. Aproperties of the 400 F. end point gasoline fraction of the raffinate, and gas voil boiling range product vfrom this extraction are listed below.

-our combination process; the loss to gas oil is about three times that obtained with the combination; and the octane number of the gasoline is 2.2 -units lower thanthat obtained by our combination process. The reversal of our proposed sequence of operations would result in a lower yield of gasoline than that obtained from HF extraction alone, which is already much lower than that from the combination process of the present invention. It is thus seen that the process of .our invention is a true combination in that it is superior to the other sequence employing the same treating steps and, also, superior to either of the individual treating steps themselves.

The accompanying iigure illustrates a suitable method for carrying out the process of the present invention. The figure shows apparatus and a .process iiow suitable for use with a dimethylformamide-water solvent. The cracked naphtha is contacted countercurrently with dimethyl- -formamide containing the requisite amount of water in tower l. The olens-saturates raffinate is water washed to remove solvent in tower Yield .2, and the extract is water washed in tower 3. v01. Wt. T The water washes are removed as bottom layers Percent Percent n 2 B12 Octane No' on s D No. (CEREM-1) from towers 2 and 3 and are sent to fractionat- Feed ing tower 5 wherein water is distilled overhead and .a dimethylformamide-water mixture with- Gaso1ineirati0n .62 .0.024 1.4459 1.8 84.4 30 drawn as bottoms and recycled to tower I. The Gas 011 fractloLm- 28 M18 14958 3'3 water washed extract is passed overhead from cracked naphtha, to give a sulfur content equivl alent to that obtained using .our combination process.

tower 3 and is sent through drier 4, e. g., a bauxite drier. The dried extract is contacted countercurrently with HF in contacting tower B. The HF extract, which forms a distinct lower liquid .layer in contacting tower 6, is sent to stripper 9 wherein HF is distilled overhead and the stripped .extract is withdrawn as a bottoms fraction. The HF Yraiiinate .from tower .6 is sent to stripper where HF' is distilled overhead, combined with the HF vapor passing overhead from tower 9 and recycled to contacting tower t. The stripped raiinate vfrom tower 'i is sent to fractionating tower v53 and separated into a low-sulfur gasoline distillate and a high sulfur gas oil fraction. The gasoline from tower 8-is blended with the olefins-saturates gasoline passing over- Yield 1 Gasoline Properties Gas HF Percent Brz Octane No. Gasoline oil Extract s m2 No (oFRR-x-i) Naphtha Feed Stock 0.275 1. 4487 45. 5 92. 9 Combination Process 85 'll 4 0.067 1. 4428- 33.8 86.6 Dimethylformamidc E raction 58 .i 0. 075 1. 4295 45. 8 80. 2 HF Extraction 62 28 l0 0. 024 1. 4459 1.8 84. 4 f HF Rainate-l-Original Feed (calcd to S content of combination process 75 28 10 0.067 86 1 Vol. percent, based on naphtha feed stock.

The advantages to be derived by the use of our combination process are manifest in the table given above. Neither dimethylformamide extraction by itself or HF extraction lby itself can approach our combination process Iin yield of high quality gasoline. Ii the gasoline from ythe HF railinate is 'blended with the original catalytica-liy cracked naphtha to give a Asulfur content equal to that resulting from the vcombination process, then a `gasoline is obtained with about the same octane number Vas that from the combination process with a loss in overall yield oi' 10%. With HF extraction alone the loss to extract is more than tw-ice `that obtained with 7-5 head from water washing tower 2 to give the finished gasoline product. If desired, the desu'lfurized aromatic hydrocarbon product passing overhead from tower 8 may be employed in the preparation of high solvency naphthas. The gas o'il fraction produced as the bottoms fraction in fractionating tower 8 is returned to the catalytic cracking step. Since this gas oil consists essentially of alkyl aromatics, it is an unusually desirable catalytic cracking charge since under catalytic cracking conditions it is dealkylated almost quantitatively, in the presence of conventional clay, SiOz-AlzOa or SiOz-MgO type catalysts, Ato provide high octane number olefins and aromatics, ,thus adding substantially to the ultimate gasoline yield from our process. If desired, fractionating tower 8 can be by-passed and the stripped HF rainate can be blended with the olens-saturates stream, optionally together with other streams boiling in the gasoline boiling range, to produce a gasoline of somewhat higher end point. The components boiling above 400 F. exert a top cylinder lubricant eifect in the blended gasoline product.

When 2,4-dimethylsulfolane is employed as the extraction solvent in the first-stage operation, it can be removed from the extract and rainate phases simply by distillation as a high boiling bottoms fraction which can be cooled and recycled to extraction tower l, thus eliminating the addition of water in towers 2 and 3 and instead employing these towers simply as fractionating columns. When ZA-dimethylsulfolane is employed as the selective extraction solvent the use of tower 5 may be dispensed with, although it may be employed intermittently to efect partial dehydration of the selective solvent before recycling it to tower I.

It will be appreciated that numerous valves, pumps, heat exchangers, etc. have been omitted from the figure in the interests of simplifying it.

Having thus described our invention, what we claim is:

1. A process for refining a cracked petroleum naphtha feed stock containing olefins, saturates, aromatics and sulfur compounds corresponding to a sulfur content of at least about 0.15 weight percent to effect substantial desulfurization thereof while minimizing the conversion of oleiins in said refining, which process comprises subjecting said feed stock to a separation treatment to produce a rst fraction comprising predominantly olenns and saturates and a second fraction comprising predominantly aromatics, sulfur compounds and a minor proportion of ole fins, based on olefins in said feed stock, treating said second fraction with liquid substantially anhydrous hydrogen iiuoride in an amount suflicient at least to form a distinct liquid acid phase at a temperature between about C. and about 100 C. Under pressure sufficient to maintain the liquid phase, thereby forming a high sulfur gas oil as one product of treatment, separating a raffinate from the hydrogen iiuoride treatment, fractionally distilling said raflinate to produce a low sulfur highly aromatic distillate boiling within the naphtha boiling range and a relatively high sulfur gas oil bottoms fraction, and blending said rst fraction and said low sulfur highly aromatic distillate to produce a low sulfur high octane number naphtha.

2. The process of claim 1 wherein said first separation treatment comprises extracting said feed stock with dimethylformamide.

3. The process of claim l wherein said separation treatment comprises extracting feed stock with 2,4-dimethylsulfolane.

4. The process of claim 1 wherein said iirst separation treatment comprises contacting said feed stock with adsorbent silica gel.

5. A process for refining a cracked petroleum naphtha feed stock containing oleiins, saturates, aromatics and sulfur compounds corresponding to a sulfur content of at least about 0.15 weight percent to effect substantial desulfurization thereof while minimizing the conversion of olens in said reiining, which process comprises subjecting said feed stock to selective extraction with between about 0.2 and about 3 volumes of first said dimethylformamide containing between about 1 and about 25 Volume percent of lwater at a 'temperature between about 10 C. and about 100 C. under pressure suiicient to maintain the liquid phase to `produce a low sulfur olens-saturates ranate and an extract comprising predominantly aromatics, sulfur compounds and a minor proportion of olens, based on olens in said feed stock, treating said extract `with liquid substantially anhydrous hydrogen fluoride in an amount sufiicient at least 'to form a distinct liquid acid phase at a temperature between about -10 C. and about 100 C. under pressure sufiicient to maintain the liquid phase, thereby forming a 'high sulfur gas oil as one product of treatinent, separating a raffinate from the hydrogen fluoride treatment, fractionally distilling said raffinate to produce a low sulfur highly aromatic distillate boiling within 'the naphtha boiling range and -a relatively high sulfur gas oil bottoms fraction, and blending said low sulfur oleiins-saturates ranate and said low sulfur, highly aromatic distillate to produce a low sulfur high octane number naphtha.

6. A process for refining a cracked petroleum naphtha feed stock containing olens, saturates, aromatics and sulfur compounds corresponding to a sulfur content of at least about 0.15 lweight percent to effect substantial desulfurization thereof while minimizing the conversion of olefins in said refining, which process comprises subjecting said feed stock to selective extraction with between about 0.5 and about 2 volumes of dimethylformamide containing between about 1 and about 10 Volume percent of water at a temperature between about 10 C. and about 50 C. under pressure suflicient to maintain the liquid phase to produce a low sulfur olefins-saturates rafnate and an extract comprising predominantly aromatics, sulfur compounds and a minor proportion of olens, based on olens in said feed stock, treating said extract with liquid substantially anhydrous hydrogen fluoride in an amount `between about 10 and about 50 volume percent, based on said extract, at a temperature between about 10 C. and about 50 C. under pressure sufficient to maintain the liquid phase, thereby forming a high sulfur gas oil as one product of treatment, `separating a raffinate from the hydrogen uoride treatment, fractionally distilling said raffinate to 'produce a low sulfur highly aromatic distillate boiling within the naphtha boiling range and a relatively high sulfur gas oil bottoms fraction, and blending said low sulfur olens-saturates raffinate and said low sulfur, highly aromatic distillate to produce a low sulfur high octance number naphtha.

'7. A process for refining a cracked petroleum naphtha feed stock containing oleflns, saturates, aromatics and sulfur compounds corresponding to a sulfur content of at least about 0.15 weight percent to effect substantial desulfurization thereof 'while minimizing 'the conversion of oleiins in said refining, which process comprises subjecting the feed stock to selective extraction with between about 0.3 and about 3 volumes of ZIA-dimethylsulfolane containing between about 1 and about l5 volume percent of water at a temperature between about 10 C. and about 100 C. under `pressure sufficient to maintain lthe liquid phase to produce a low sulfur olens-saturates rafnate and an extract comprising predominantly aromatics, sulfur compounds and a minor proportion of oleflns, based -on olens in said feed stock, treating said extract with liquid substantially anhydrous hydrogen fiuoride in an amount sufiicient at least to form a distinct liquid a-cid phase at a temperature between about C. and about 100 C. under pressure surdeient to maintain the liquid phase, thereby forming a high sulfur gas oil as one product of treatment, separating a rainnate from the hydrogen uoride treatment, fractionally distilling said rainate to produce a low sulfur highly aromatic distillate boiling within the naphtha boiling range and a relatively 'high sulfur gas oil bottoms fraction, and blending said low sulfur olens-saturates raflinate and said low sulfur, highly aromatic distillate to produce a low sulfur high octane number naphtha.

8. A process for rening a cracked lpetroleum naphtha feed stock containing olens, saturates, aromatics and sulfur compounds correspon-ding to a sulfur content of at least about,0.15 weight percent to effect substantial desulfurization thereof while minimizing the conversion of olens in said refining, which process comprises subjecting the feed stock to selective extraction with between about 0.5 and about 1 volume of 2,4dimethylsuliolane containing between about l and about 5 Volume percent of water at a temperature of about C. `under pressure sufficient to maintain the liquid phase to produce a low' sulfur olens-saturates rainate and an extract comprising predominantly aromatics, sulfur compounds and a minor proportion of olens, based 12 on olefins in said feed stock, treating said extract with liquid substantially anhydrous hydrogen fluoride in an amount between about 10 and about Volume percent, based on Said extract, at a temperature between Aabout 10 C. and about 50 C. under pressure sumcient to maintain the liquid phase, thereby forming a high sulfur gas oil as one 4product of treatment, separating a rainate from the hydrogen uoride treatment, fractionally distilling said raiinate to produce a low sulfur highly aromatic distillate boiling within the naphtha boiling range and a relatively high sulfur gas oil bottoms fraction, and blending said low sulfur olens-saturates raffinate and said low sulfur, highly aromatic distillate to produce a low sulfur high octane number naphtha.

`9. The process of claim 1 wherein said first separation treatment comprises extracting said feed stock with a `dialkylfor'mamidel References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,166,140 Hansley July 18, 1939 2,402,799 Arnold et al June 25, 1946 2,440,258 Elliott et al. Apr. 27, 1948 2,464,520 Lien et al Mar. 15, 1949 2,479,238 Holm et a1 Aug. 16, 1949 2,501,064 Lien et al Mar. 21, 1950 2,608,519 Deters et al Aug. 26, 1952 

1. A PROCESS FOR REFINING A CRACKED PETROLEUM NAPHTHA FEED STOCK CONTAINING OLEFINS, SATURATES, AROMATICS AND SULFUR COMPOUNDS CORRESPONDING TO A SULFUR CONTENT OF AT LEAST ABOUT 0.15 WEIGHT THEREOF WHILE MINIMIZING THE CONVERSION OF OLEFINS IN SAID REFINING, WHICH PROCESS COMPRISES SUBJECTING SAID FEED STOCK TO A SEPARATION TREATMENT TO PROCUDE A FIRST FRACTION COMPRISING PREDOMINANTLY OLEFINS AND SATURATES AND A SECOND FRACTION COMPRISING PREDOMINANTLY AROMATICS, SULFUR COMPOUNDS AND A MINOR PROPORTION OF OLEFINS, BASED ON OLEFINS IN SAID FEED STOCK, TREATING SAID SECOND FRACTION WITH LIQUID SUBSTANTIALLY ANHYDROUS HYDROGEN FLUORIDE IN AN AMOUNT SUFFI- 